1. Field of the Invention
The present invention relates to a television broadcast signal receiving system which can receive television broadcast signals in the UHF band and the VHF band, and more particularly, to a television broadcast signal receiving apparatus having a channel auto scanning (channel auto setting) function using a multiple directional antenna and an antenna apparatus suitable to the television broadcast signal receiving apparatus.
2. Description of the Related Art
In North America where the ATSC digital television broadcast (hereinafter, abbreviated as TV broadcast) is carried out, TV broadcast signals are transmitted from-various directions because large cities are scattered across the plain area and a number of broadcasting station exist. In such environment, viewers who receive the TV broadcast signals need to adjust the receiving direction of the antenna in the direction of a broadcasting station in which the program they want to watch is broadcasted. Consequently, multiple directional antennas such as a smart antenna and the like are in practical use (for example, see Tokukai 2005-117608 and Tokukai 2001-036327 (Tokkyo 3625155)).
Moreover, a technique relating to an auto scanning function which can automatically set the receiving direction of the antenna in which the TV broadcast signal of the channel selected by a viewer can be received in the best condition is proposed (for example, see Tokukaihei 06-113220 and Tokukai 2001-68627). Normally, antennas of broadcasting stations, i.e. positions of broadcasting towers do not vary. Therefore, scanning is carried out in a plurality of directions (for example, 16 directions) for each channel to set the direction having the best receiving condition as the receiving direction of the channel.
According to the EIA-909 standard, it is defined that the smart antenna has receiving directions in each of 16 directions into which a circle is divided. Meanwhile, a digital TV broadcast signal receiving apparatus which complies with the EIA-909 standard is constructed so as to control the receiving directions with respect to all 16 directions in which the signal can be received by the smart antenna.
By the way, in a television broadcast signal receiving apparatus, a channel auto scanning needs to be carried out in order to receive broadcast signals from each broadcasting station, and the viewers prefer to complete the channel auto scanning as quickly as possible. However, when auto scanning of channels is executed by using the smart antenna and the auto scanning function which are disclosed in the above mentioned prior art, there is a problem that it takes a long time to carry out the setting because the scanning is carried out in all 16 directions for each channel whether the TV broadcast signal is in the VHF band or the UHF band.
On the other hand, in recent years, digitalization of terrestrial broadcasting is rapidly progressing throughout the world. The terrestrial digital broadcasting is broadcasted in tandem with the existing UHF analog broadcasting. However, at each allotted channel frequency, 5 or 6 programs can be transmitted simultaneously. Therefore, there is an advantage where the problem of restricted frequency can be eliminated by using vacant-frequencies in various areas. Moreover, it is decided that the terrestrial analog broadcasting is to be terminated and shifts to the terrestrial digital broadcasting completely in few years. Consequently, broadcasting using the VHF band is to be reduced and terminated in the future.
Under such situation, the number of channels which are not received (vacant-channel) increases. Therefore, more needless time may be spent even when the above mentioned prior art is used to set a channel in the VHF band.
In an antenna apparatus in which a multiple directional antenna for the UHF band and a unidirectional antenna for the VHF band are provided, which antenna is used and how wide the frequency band which can be covered by the antenna are different according to the specification of an antenna element. Therefore, when carrying out the channel auto scanning process in the television broadcast signal receiving apparatus, the best suitable frequency range (range of channels which can be received) is not necessarily always set for each antenna.